Exploring the Universe with Telescopes & Light

Some Hands-On Optics

Hands-On Optics Inquiry-based activities Collaboration International Society for Optical Engineering Optical Society of America National Optical Astronomy Observatory National Science Foundation http://www.hands-on-optics.org

Hands-On Optics Terrific Telescopes Selected three activities Significantly abbreviated Module 3: Magnificent Magnifications sciencefirst.com $475 classroom kit

Simple Magnifiers Materials Always handle lenses by edges Thinner lens Thicker lens Astronomy picture Always handle lenses by edges

Simple Magnifiers Hold a lens about an inch away from picture. Move lens toward and away from picture. Trade lenses and try it with other types of lenses.

Simple Magnifiers Which lens magnifies most? At what distance does magnification cease?

Simple Magnifiers Which lens magnifies most? At what distance does magnification cease? Thinner lens – 20 cm focal length Thicker lens – 7.5 cm focal length

Bends at each interface!

Lenses & Lasers & Lights Materials Various lenses Various lasers Bright image source White paper Always handle lenses by edges

Lenses & Lasers & Lights Shine laser through various parts of a lens Observe the change in refraction Which part of the lens refracts more? Shine two lasers or laser level through lens Move lens toward and/or away from laser(s) Can you get light points to converge? Can you measure focal length of lens?

Lenses & Lasers & Lights Line up a bright image source – lens – white paper Try to project image onto white paper. It works best when paper is in shadow. Adjust lens position to focus image. Is image upright or inverted? What is paper-lens distance? How does it compare to the lens focal length?

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Hands-On Optics: Refracting Telescope I

Build a Refracting Telescope I Materials Thinner lens (20 cm focal length) Thicker lens (7.5 cm focal length) Always handle lenses by edges

Build a Refracting Telescope I Hold the thinner lens in front of your eye with the thicker lens about a foot away. Examine a distant object by looking through both lenses. Try the thicker lens in front of your eye with the thinner lens about a foot away.

Build a Refracting Telescope I Which arrangement of lenses was easier to get a clear view? Which arrangement of lenses magnified more?

Hands-On Optics: Refracting Telescope II

Build a Refracting Telescope II Materials Cardboard tubes (inner and outer) Plastic bag of optics Large lens Small lens Cardboard washer (disk) Cardboard spacer (cylinder) Plastic cap Foam insert Always handle lenses by edges

Build a Refracting Telescope II How are these lenses different from the previous lenses? Why are there two cardboard tubes? Can a working telescope be built out of such simple materials?

Build a Refracting Telescope II Put curved side of large lens against end of outer tube. Add washer and cap. Push small lens into foam eyepiece holder. Slide cardboard spacer into foam eyepiece holder against the flat side of small lens. Slide foam eyepiece holder into inner tube with cardboard spacer toward end.

Build a Refracting Telescope II How is refraction different for a plano-convex lens than for a double convex lens? What knowledge or skills would be important in making telescopes? How might professional telescopes differ from these simple models?

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